Coherence a measure of the brain networks: past and present

Abstract

Brian connectivity describes the networks of functional and anatomical connections across the brain. The functional network communications across the brain networks dependent on neuronal oscillations. Detection of the synchronous activation of neurons can be used to determine the wellbeing or integrity of the functional connectivity in the human brain networks. Well-connected highly synchronous functional activity can be measured by Electroencephalography (EEG) or Magnetoencephalography (MEG) and then analyzed with several types of mathematical algorithms. Coherence is one mathematical method that can be used to determine if two or more sensors, or brain regions, have similar neuronal oscillatory activity with each other. Since the 1960's, coherence has generally been assessed on the similarity of the frequency content across EEG sensors. Recently coherence, after it has been imaged in the brain, has been used to assess how coherent or connected specific locations in the brain are networked together in several different neurological disorders. Statistical analysis can then be performed on the coherence results to verify evidence of normal or abnormal network activity in a patient. In this review we highlight how functional brain connectivity is assessed in Source space using coherence technique measured by MEG.

Coherence: The Measurement and Application of Brain Connectivity

“…The remaining sections of this manuscript will provide additional details of the NCC framework and its clinical application. Additionally, we will discuss specific methods of objectively measuring and/or modulating brain network connectivity, focusing primarily on a metric referred to as EEG coherence (Bowyer, 2016).…”

“…Thus, the notion of functional connectivity has gained great traction in recent years (Glasser et al, 2016;Smith et al, 2013), including spawning large-scale projects to systematically map the human functional brain networks and their key nodes (http://www.humanconnectome.org/; Glasser et al, 2016). The term functional connectivity is used to describe the correlated neuronal activity of these various regions (Bowyer, 2016). However, this term is not only conceptual but also refers to the measurement basis of brain connectivity using fMRI and EEG methodologies.…”

“…Functional connectivity refers to the cross-temporal correlation of measured brain activity in different regions of the brain (Bowyer, 2016;Honey et al, 2009). While much of the work in defining functional connectivity has utilized resting-state fMRI (RS-fMRI; e.g., Smith et al, 2013), as noted above, more temporally sensitive methods such as EEG and MEG are also necessary to evaluate how functional connectivity might change over brief timescales (Bowyer, 2016; also see discussion of functional versus effective connectivity in Friston, 2011). Coherence is one commonly used metric for deriving functional brain connectivity in EEG, which will be discussed in detail below.…”

“…It incorporates information on synchrony including both amplitude and phase, but is independent of power (Bowyer, 2016).…”

Gamma Coherences in the Default Mode Resting State as a Measure of Consciousness Level

“…The squared coherence is the squared correlation coefficient between the cyclical components in two series at the respective frequency. It is the product of the cross-amplitude values after squaring them and dividing by the product of the spectrum density estimates for each series (Bowyer, 2016). It is well known that the squared coherence value decreases with increasing distances between the electrodes.…”